Variable displacement rotary hydraulic machines

ABSTRACT

A variable displacement pump or motor comprises a gerotor assembly, the inner and outer elements of which can be displaced axially in relation to one another, so that the capacity of the gerotor chamber can be varied. The gerotor chamber is defined by a locating ring, and a pair of end plugs which are respectively keyed to the inner and outer gerotor elements for rotation therewith. One end plug and one gerotor element are fixed in a certain axial position, while the other end plug and gerotor element are located by the locating ring which is axially movable.

United States Patent [191 Charron VARIABLE DISPLACEMENT ROTARY HYDRAULIC MACHINES Inventor: Charles S. Charron, Clarkson,

Ontario, Canada Assignee: Aplitec Limited, Clarkson, Ontario,

Canada Filed: Nov. 3, 1972 Appl. No.2 303,356

References Cited UNITED STATES PATENTS 10/1949 Hill et al. 418/21 1 Apr. 23, 1974 3,687,578 8/1972 White et al. 418/21 Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Ridout & Maybee [5 7] ABSTRACT A variable displacement pump or motor comprises a gerotor assembly, the inner and outer elements of which can be displaced axially in relation to one another, so that the capacity of the gerotor chamber can be varied. The gerotor chamber is defined by a locating ring, and a pair of end plugs which are respectively keyed to the inner and outer gerotor elements for rotation therewith. One end plug and one gerotor element are fixed in a certain axial position, while the other'end plug and gerotor element are located by the locating ring which is axially movable.

7 Claims, 9 Drawing Figures iATENTEDAPR 23 mm SHEET 4 [1F 7 f i t,

VARIABLE DISPLACEMENT ROTARY HYDRAULIC MACHINES components being either directly connected or situated at different locations andinterconnected by pipes or hoses for conveying the hydraulic fluid. Machines for this purpose include pumps and motors of the axial piston, radial piston, vane, and gear types; of these, machines the piston andthe vane types suffer from the disadvantages of being relatively expensive,of being susceptible to wear on account of the close fit between the sliding surfaces, and of requiring a well filtered operating fluid. The gear type machines are relatively inexpensive, and on account of fairly large tolerances are less susceptible to wear than the other types and can function when the operating fluid contains a high concentration of contaminants. However, unlike the piston and vane types of machine, gear type machines cannot be contructed as variable displacement pumps and motors and so are not suitable for. use in variable hydrostatic transmissions.

The present invention is based on an adaptation of the gerotor principle whereby to provide a variable displacement pump or motor which shares the principal advantages of gear type machines.

The gerotor principle has been known for many years and was perfected in the 1930s by W. H. Nichols. A gerotor assembly essentially comprises a pair, of intermeshing, inner and outer gear-like elements whose rotational axes are offset so that one axis orbits around the other, the outer element having internal teeth in the form of part-circular lobes, and the inner element having external teeth which are one less in number. than the lobes and matched to the shape of the lobes so as to make rolling contact. The elements are located in a cylindrical housing comprising alocating ring, which defines the rotational axes of the gears, and a pair of end walls or plugs. The locating ring and end walls, or plugs, define a chamber (herein referred to as the gerotor chamber) in which the gear-like elements operate, the inner element being rotatable with a rotary shaft journalled in one end wall, and hydraulic fluid being supplied to and from the gerotor via ports which' are usually in the other end wall.

Existing gerotor devices are essentially of the fixed displacement type. ACCQrding to the present invention,

however, a variable displacement rotary hydraulic machine includes a gerotor assembly wherein means are provided for effecting relative axial displacement of the gerotor elements so as to vary the capacity of the gerotor chamber.

In order that the invention may be readily understood, two embodiments of the invention will now be described by way of example with reference to the ac companying drawings. In the drawings:

FIG. 1 is a part-sectional side elevation of a hydro-- FIG. 1a is an enlarged sectional view of a detail of FIG. 1 showing the positions of the gerotor gears when the capacity of the gerotor chamber has been reduced;

FIG. 2 is a section on line 2-2 in FIG. 1; FIG. 3 is a section on line 3-3 in FIG. 1;

FIG. 4 is a plan view of the detail shown in FIG. 3;

FIG. 5 is an exploded perspective view showing the essential elements of a gerotor assembly;

FIG. 6 is a schematic diagram of a hydrostatic transmission set in'accordance with the invention;

FIG. 7 is a longitudinal sectional view of a modified variable displacement pump in accordance with the invention, the section being taken on line 7-7 in FIG. 8; and

FIG. 8 is'as'ection 'on line'8-f8 in FIG. 7.

DESCRIPrIoN- rHE P EERRED EMBODIMENTS General Before examiningthe details of construction of the rotary hydraulic machines to which this invention relates, it will be instructive to consider the hydrostatic transmission set shown diagrammatically in FIG. 6, which representsone application of the invention. The hydrostatic transmission set comprises a pair of machines 10, 11 mounted in a common casing 12. The machine 10 operates as a variable displacement pump, and the machine 11 operates as a motor receiving its operating fluid from the pump; A source of hydraulic fluid is constituted by a reservoir 13, a supply duct 14 leading from the reservoir to the pump inlet 15. The pump outlet l6 is connected by a duct 17 to the motor inlet 18, and the outlet 19 of the motor is connected to a return duct 20 by which the fluid is returned to the reservoir 13. A'tilter 21 is fitted to the inlet end of the supply duct 14, to ensure a clean supply of operating fluid to the pump. A pipe 22 permits any fluid leakage at the pump to return to the reservoir.

The operating pressure of the-hydraulic fluid at the inlet to the motor is limited by a pressure release valve 23 positioned in a flow path24 between the duct 1 and the reservoir 13.

The pump-l0 and motor 11 have rotary shafts (not shown in FIG. 6) providing the input and output of the transmission. As the pump is driven from an external power source it generates a supply of pressurized fluid for the motor whereby to drive the motor, the operating fluid circulating as indicated by the arrows. The transmission ratio is determined by the relative settings of the variable displacement machines 10 and 11.

VARIABLE DISPLACEMENT FEATURE The variable displacement feature of each of the mament orbits around the rotational axis of the inner element. A first plug 27 is formed with an inner peripheral edge 28 conforming to the shape of the inner element whereby it is keyed to the inner element 25, for rotation therewith. Similarly a second plug 29 has an outer peripheral edge conforming to the shape of the outer element 26 whereby it is keyed to the outer element for rotation therewith. The plug 29 is formed with seven (in this example) ports 30, which cooperate cyclically with an inlet duct 31 and an outlet duct 32 of a valve body 33. The valve body is secured against axial and rotational movement by bolts 34.

A first ring member 35 and a second ring member 36 are bolted together with the interposition of a sealing ring 37 to form a composite locating ring. The locating ring being mounted, as hereinafter described, so as to be axially displaceable. The locating ring encompasses the outer gerotor element 24 and the plugs 27, 29, so as to locate these plugs and element with respect to the inner gerotor element 25. The locating ring and the plugs define a gerotor chamber in which the gerotor elements operate. The plug 27 is located axially by being clamped between the ring members 35, 36, and the outer element 34 is located axially by being disposed between the plug 27 and an annular surface 38 in the ring member 35. Therefore, when the locating ring is axially displaced the outer gerotor element 34 and plug 27 are displaced relatively to the inner element 25 and plug 29; the gerotor chamber is thus of variable capacity.

For effecting axial displacement of the locating ring the ring member 36 is formed with external screw threads 39 which engage an internally threaded collar 40. The collar 40 is formed with external transverse threads 41 which engage a worm gear 42, the latter being mounted in the machine casing (see FIG. 1a) and being rotatable. in this way a very fine control of the relative axial positions of the gerotor elements is ensured.

DESCRlPTION OF THE PREFERRED EMBODIMENTS Reference will now be made to FIGS. 1 to 4, which show details of the construction of the first embodiment. The stationary casing 12 is. provided with a pair of end walls. One end wall is formed by a bell member 43 which is bolted to the casing by bolts 44, a seal housing 45 being bolted in turn to the bell member by bolts 46. The input shaft 47 of the transmission set extends through the end wall and is journalled in bearings 48 for rotation about its axis. The shaft 26 to which the inner gerotor element 25 is keyed forms an extension of the input shaft 47 and is coaxial with it. The other end wall of the casing 12 is formed by a partition structure 49 which is provided with internal passages constituting the ducts 14, 17. Between the end walls of the casing 12 the locating ring 35, 36 is located axially by a spigot-like portion 50 of the bell member 43. It will be noted that the two ring members are secured axially by bolts 51. The locating ring is secured against rotation by means of a key 52 projecting inwardly from the wall of the casing 12 and engaging in an axially extending slot 53 in the locating ring. As previously described, the locating ring can be moved axially for varying the capacity of the gerotor chamber, and hence the output of the pump, by the threaded collar 40 and worm gear 42.

The motor 11 comprises a second gerotor assembly, the inner element 54 of which is keyed to a rotary shaft 55 constituting the output shaft of the transmission set.

The rotary shaft 55 is journalled in bearings 56 for rotation about its axis, which is coaxial with the input shaft 47, and extends through a second bell-shaped seal housing 57. The seal housing 57 is bolted to a flanged member 58 by bolts 59, the flanged member 58 being bolted to one end of the casing 12 by bolts 60. The outer element 53 of the second gerotor assembly is constrained by a locating ring 61, the latter being located between end plugs 62, 63, and thus defining the chamber of the second gerotor assembly. The end plug 62 is formed with an inlet 64 and an outlet 65, the positions of which relative to the orientation of the eccentric locating ring 61 can be varied by a worm gear 66 which engages external transverse threads on the locating ring. By rotation of the locating ring the positions of the motor inlet and outlet can be intercharged, thus affording a means to reverse the motor.

In the embodiment shown in FIGS. 7 and 8, the outer gerotor element 67 is coaxial with the drive shaft 68 and the inner gerotor element 69 rotates about an axis which orbits around the axis of the drive shaft. The inner element 69 is splined to one end of a universal shaft 70 by splines 71, the other end of the universal shaft being splined to the inner surface of a hollow end of the drive shaft 68. The ends of the universal shaft respectively bear against a pad 72, which forms an integral part of the end plate 73 of the housing 74, and against a spring-loaded pad 75 inside the hollow end of the shaft 68. The gerotor elements 67, 69 operate within a gerotor chamber defined by a locating ring 76, a first end plug 77 keyed to the inner element 69 for rotation therewith and a second end plug 78 keyed to the outer element 69 for rotation therewith. A second end plate 79 is bolted to the housing 74 by bolts 80. The end plate 79 is bell-shaped to accommodate an annular enlargement 81 of the drive shaft 68, and is formed with a fluid inlet 82 and a fluid outlet 83. The annular enlargement 81 has a pair of circumferential grooves 84, 85 cooperating with the inlet 82 and outlet 83, respectively; an inlet duct 86 extends from the groove 84 to an inlet port 87 in the end plug 78, and an outlet duct 88 extends from the groove 85 to an outlet port 89 in the end plug.

The locating ring 76 comprises a pair of ring members which are secured axially, as in the preceding embodiment. For varying the output of the pump (or motor, if the machine is adapted to operate as a motor) the capacity of the gerotor chamber may be varied by axially displacing the locating ring 76. For this purpose one end of the locating ring is connected to an axially extending adjustment shaft 90, which is threaded into a bush 91 at one end of the housing 74. As in the preceding example, rotational movement of the locating ring 76 is prevented by a key member 92 engaging in an axially extending slot 93 in the locating ring.

What we claim as our invention is:

l. A variable displacement rotary hydraulic machine comprising 0 a. a stationary casing having first and second end walls;

b. a rotary shaft journalled in the first end wall for rotation about a predetermined axis;

c. a gerotor assembly mounted within the casing, the

gerotor assembly comprising i. intermeshing inner and outer gerotor elements, the inner element being connected to the shaft for rotation therewith,

ii. a first plug engaging the inner element for rotation therewith,

iii. a ported second plug engaging the outer gear for rotation therewith,

iv. an axially displaceable locating ring encompassing the outer element and the plugs for locating the same with respect to the inner element, the outer element and first plug engaging the locating ring for axial displacement therewith,

v. the plugs and locating ring defining a gerotor chamber of variable capacity;

d. valve means secured to one end wall of the casing, the valve means providing inlet and outlet ducts communicating with the ports of the second plug for leading hydraulic fluid to and from the gerotor chamber;

e. means cooperating with the locating ring for effecting axial displacement thereof whereby to vary the effective capacity of the gerotor chamber; and

f. means for preventing rotational movement of the locating ring within the casing.

2. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the inner element is connected to the rotary shaft for rotation about said predetermined axis, the outer element being constrained by the locating ring to rotate about an axis which orbits around said predetermined axis.

3. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the outer element is located by the locating ring in coaxial relation with said rotary shaft, the inner element being connected to said shaft by a universal coupling and being constrained by said first plug to .rotate about an axis which orbits around said predetermined axis.

4. In combination with a variable displacement rotary hydraulic machine as claimed in claim 1, the machine being adapted to operate as a variable displacement pump: a source of hydraulic fluid, a rotary hydraulic motor mounted on the second end wall of said casing, the motor having a fluid inlet and fluid outlet, a supply duct connecting said source with said inlet duct of the pump, means connecting said outlet duct of the pump with the inlet of the hydraulic motor, and a return duct connecting the outlet of the hydraulic motor with said source.

5. The combination claimed in claim 4, wherein the hydraulic motor comprises a rotary motor shaft journalled for rotation about said predetermined axis, and a gerotor assembly comprising intermeshing inner and outer gerotor elements operating in a gerotor chamber within the motor casing, the inner element being connected to the motor shaft for rotation therewith.

6. The combination claimed in claim 5, including means for reversing the fluid connections to the motor for effecting reversal of the motor.

7. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the locating ring is formed with an axially extending threaded flange, said means for effecting axial displacement of the locating ring comprising a worm gear journalled in the casing and engaging said flange. 

1. A variable displacement rotary hydraulic machine comprising a. a stationary casing having first and second end walls; b. a rotary shaft journalled in the first end wall for rotation about a predetermined axis; c. a gerotor assembly mounted within the casing, the gerotor assembly comprising i. intermeshing inner and outer gerotor elements, the inner element being connected to the shaft for rotation therewith, ii. a first plug engaging the inner element for rotation therewith, iii. a ported second plug engaging the outer gear for rotation therewith, iv. an axially displaceable locating ring encompassing the outer element and the plugs for locating the same with respect to the inner element, the outer element and first plug engaging the locating ring for axial displacement therewith, v. the plugs and locating ring defining a gerotor chamber of variable capacity; d. valve means secured to one end wall of the casing, the valve means providing inlet and outlet ducts communicating with the ports of the second plug for leading hydraulic fluid to and from the gerotor chamber; e. means cooperating with the locating ring for effecting axial displacement thereof whereby to vary the effective capacity of the gerotor chamber; and f. means for preventing rotational movement of the locating ring within the casing.
 2. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the inner element is connected to the rotary shaft for rotation about said predetermined axis, the outer element being constrained by the locating ring to rotate about an axis which orbits around said predetermined axis.
 3. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the outer element is located by the locating ring in coaxial relation with said rotary shaft, the inner element being connected to said shaft by a universal coupling and being constrained by said first plug to rotate about an axis which orbits around said predetermined axis.
 4. In combination with a variable displacement rotary hydraulic machine as claimed in claim 1, the machine being adapted to operate as a variable displacement pump: a source of hydraulic fluid, a rotary hydraulic motor mounted on the second end wall of said casing, the motor having a fluid inlet and fluid outlet, a supply duct connecting said source with said inlet duct of the pump, means connecting said outlet duct of the pump with the inlet of the hydraulic motor, and a return duct connecting the outlet of the hydraulic motor with said source.
 5. The combination claimed in claim 4, wherein the hydraulic motor comprises a rotary motor shaft journalled for rotation about said predetermined axis, and a gerotor assembly comprising intermeshing inner and outer gerotor elements operating in a gerotor chamber within the motor casing, the inner element being connected to the motor shaft for rotation therewith.
 6. The combination claimed in claim 5, including means for reversing the fluid connections to the motor for effecting reversal of the motor.
 7. A variable displacement rotary hydraulic machine as claimed in claim 1, wherein the locating ring is formed with an axially extending threaded flange, said means for effecting axial displacement of the locating ring comprising a worm gear journalled in the casing and engaging said flange. 